Artist that is revolutionary (6)
I believe the answer is:
turner
This clue is a double definition.
'artist' is the first definition.
(painter JMW Turner)
'that is revolutionary' is the second definition.
(something which revolves)
(Other definitions for turner that I've seen before include "Fighting Temeraire artist" , "Popular English artist" , "Artist - wheel?" , "Painter of seascapes" , "He painted Rain, Steam and Speed - The Great Western Railway" .)